1. Technical Field
The present invention generally relates to a circuit and method for input side impedance matching of a power amplifier in an electronic device. In particular, the present invention relates to an impedance transformer network for synthesizing impedance at an input of the power amplifier.
2. Background Art
In the area of Radio-Frequency (RF) circuit design, the need to achieve an impedance match at the load and source ends of the circuit is great. The failure to achieve an impedance match is especially problematic in the design of electronic equipment (e.g. audio, wireless communications, etc.), where un-matched impedances can substantially reduce sound quality. Such impedance matching is traditionally accomplished by transforming either the load end impedance or the source end impedance to match the other.
To date, various transforming networks have been implemented for achieving transformation in an RF circuit. Typically, such systems utilize capacitors, inductors, and resistors along with transmission lines to achieve the intended matching. One example of such a system is an LC match comprised of an inductor xe2x80x9cLxe2x80x9d and capacitor xe2x80x9cC.xe2x80x9d However, when used for input side matching of a power amplifier, the LC match often results in a reduced signal swing (i.e., reduced ratio of signal voltage at the amplifier input to signal voltage at the signal source).
In order to overcome the reduce signal swing problem, some circuits are designed with an additional input stage pre-driver(s) to size down and achieve the required input impedance. This is often the case with CMOS based circuits where adequate input drive signal is important. However, the use of additional stages implies more interstage matching, which has an impact on design reliability and cycle time.
In view of the foregoing, there exists a need for an improved circuit and method for input side impedance of a power amplifier in an RF circuit (e.g., that is implemented in an electronic device). In addition, there exists a need for such a circuit to include an impedance transformer network for synthesizing the source side impedance at the amplifier input. There also exists a need for such a circuit and method to increase signal swing without requiring additional stages (e.g., pre-drivers).
The present invention overcomes the drawbacks of existing systems by providing a circuit and method for input side impedance matching of a power amplifier in an electronic device. In particular, the present invention includes an impedance transformer network that comprises a negative resistor in series with an inductor for synthesizing the source side impedance at the input side of the power amplifier.
According to a first aspect of the present invention, a circuit for input side impedance matching of a power amplifier in an electronic device is provided. The circuit comprises: (1) a source for providing a signal, wherein the signal has a predetermined impedance; and (2) an impedance transformer network joined in parallel with the source, wherein the network comprises a negative resistor in series with an inductor, and wherein the network synthesizes the predetermined impedance at an input of the power amplifier.
According to a second aspect of the present invention, a circuit for input side impedance matching of a power amplifier in an electronic device is provided. The circuit comprises: (1) a source for providing a signal, wherein the signal has a predetermined impedance; (2) an impedance transformer network joined in parallel with the source, wherein the network comprises a negative resistor in series with an inductor; and (3) wherein a value of the negative resistor is selected to synthesize the predetermined impedance at an input of the power amplifier, and wherein the inductor has a reactance equal to a capacitance of the device at a required frequency of operation.
According to a third aspect of the present invention, a method for matching impedance at an input of a power amplifier in an electronic device is provided. The method comprises the steps of: (1) providing a signal from a source, wherein the provided signal has a predetermined impedance; (2) joining an impedance transformer network in parallel with the source, wherein the network comprises a negative resistor in series with an inductor; and (3) selecting a value for the negative resistor so that the predetermined impedance is synthesized at the input of the power amplifier.
Therefore, the present invention provides a circuit and method for input side impedance matching of a power amplifier in an electronic device. The present invention reduces the problems associated with unmatched impedances and reduced signal swing.